Polycarbonate resins have excellent heat resistance, mechanical properties, and electrical properties, and they are widely used, for example, in materials for automobiles, materials for electrical and electronic equipment, housing materials, and materials for the manufacture of parts in other fields of industry. In particular, polycarbonate resin compositions imparted with flame resistance are most suitably used as materials for manufacturing computers, notebook type personal computers, cell phones, portable terminals, printers, copiers, and other office automation and data processing equipment.
In the past, halogen-based flame retardants and phosphorus-based flame retardants have been blended into polycarbonate resins as methods of imparting flame resistance thereto.
However, polycarbonate resin compositions containing halogen-based flame retardants, which comprise chlorine and bromine, tend to have problems such as a decrease in thermostability, corrosion of the forming molds and screws of the molding machines during the molding process, and the like. Moreover, polycarbonate resin compositions containing phosphorus-based flame retardants tend to have problems such as interference with the high level of transparency that is the hallmark of polycarbonate resins, as well as a decrease in impact resistance and thermostability, so their use therein is limited. In addition, because halogen-based flame retardants and phosphorus-based flame retardants can cause environmental pollution when the manufactured products are discarded and collected, recently it has become desirable to impart flame resistance without using these kinds of flame retardants.
Under such circumstances, a large number of metal salt compounds typified by alkali metal salts of organic acids and alkaline earth metal salts of organic acids are being investigated as useful flame retardants. When an organometallic salt compound is used as a flame retardant, efficacy can be obtained with a relatively small amount thereof, and flame resistance can be imparted without a loss of the intrinsic properties of polycarbonate resins such as impact resistance and other mechanical properties, heat resistance, and electrical properties.
As techniques for imparting flame resistance to a polycarbonate resin using a metal salt compound, for example, methods have been proposed wherein flame resistance is imparted to an aromatic polycarbonate resin using an alkali metal salt compound of a perfluoroalkane sulfonic acid such as the method using an alkali metal salt of a C4-8 perfluoroalkyl sulfonic acid (see Patent literature 1), and the method of including therein an alkali metal salt of a C1-3 perfloroalkane sulfonic acid (see Patent literature 2); and methods have been proposed wherein flame resistance is imparted to a polycarbonate resin composition using an alkali metal salt of an aromatic sulfonic acid such as the method of including therein a sodium salt of a halogen free aromatic sulfonic acid (see Patent literature 3), and the method of including therein a potassium salt of a halogen free aromatic sulfonic acid (see Patent literature 4).
These metal salt-based flame retardant compounds have relatively good compatibility with the polycarbonate resin and flame retardant properties, and they have few adverse effects on the hue of the polycarbonate resin. Therefore, although they are excellent flame retardants and a level of compatibility that does not cause problems from a practical standpoint, these compounds (more specifically, the use of a compound such as potassium nonafluorobutane sulfonate, sodium nonafluorobutane sulfonate, and potassium diphenylsulfone sulfonate is particularly preferred) are essentially hydrophilic and do not have good compatibility with polycarbonate resins.
Although flame resistance may be high, when compatibility with the polycarbonate resin is low, the amount of haze increases, which imposes the limitation that these flame retardants cannot be used in fields requiring high transparency and in products requiring an upscale image with no clouding. For example, because trifluoro methanesulfonates have a short molecular chain, they have better flame resistance than other metal salts, but they are difficult to use because the haze value becomes too large.
Moreover, if an attempt is made to add more metal salt-based flame retardant to increase flame resistance, deterioration in the haze value becomes too conspicuous beyond a certain level, and the content cannot be increased any farther. In addition, increasing the amount of flame retardant tends to have an adverse effect on the hue of the polycarbonate resin composition, which is also undesirable.
For example, for a transparent, flame retardant polycarbonate resin composition, about 0.08-0.1 mass % of potassium nonafluorobutane sulfonate may be added to prevent color tone deterioration and assure transparency. Even in such cases, however, the hydrophilic potassium nonafluorobutane sulfonate coagulates and causes clouding in the thicker sections that cool slowly during injection molding, so the use thereof is limited in products that have thick sections.
Moreover, when a metal salt-based flame retardant is added to a glass fiber-reinforced polycarbonate resin material wherein glass fibers have been mixed into the polycarbonate resin to further increase strength, there is a problem in that the strength and rigidity of the polycarbonate resin decrease.
In addition, when a metal salt-based flame retardant is added to a polycarbonate resin material wherein an elastomer has been mixed into the polycarbonate resin to impart a high level of impact resistance, there is a problem in that the polycarbonate resin or the elastomer will tend to yellow easily, and the color tone will deteriorate.